| Message ID | 20240309202445.work.165-kees@kernel.org (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | 9c573cd313433f6c1f7236fe64b9b743500c1628 |
| Headers | show |
| Series | randomize_kstack: Improve entropy diffusion | expand |
On Sat, 09 Mar 2024 12:24:48 -0800, Kees Cook wrote: > The kstack_offset variable was really only ever using the low bits for > kernel stack offset entropy. Add a ror32() to increase bit diffusion. > > Applied to for-next/hardening: [1/1] randomize_kstack: Improve entropy diffusion https://git.kernel.org/kees/c/9c573cd31343
diff --git a/include/linux/randomize_kstack.h b/include/linux/randomize_kstack.h index 5d868505a94e..6d92b68efbf6 100644 --- a/include/linux/randomize_kstack.h +++ b/include/linux/randomize_kstack.h @@ -80,7 +80,7 @@ DECLARE_PER_CPU(u32, kstack_offset); if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \ &randomize_kstack_offset)) { \ u32 offset = raw_cpu_read(kstack_offset); \ - offset ^= (rand); \ + offset = ror32(offset, 5) ^ (rand); \ raw_cpu_write(kstack_offset, offset); \ } \ } while (0)
The kstack_offset variable was really only ever using the low bits for kernel stack offset entropy. Add a ror32() to increase bit diffusion. Suggested-by: Arnd Bergmann <arnd@arndb.de> Fixes: 39218ff4c625 ("stack: Optionally randomize kernel stack offset each syscall") Signed-off-by: Kees Cook <keescook@chromium.org> --- Cc: Jeremy Linton <jeremy.linton@arm.com> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org> Cc: linux-hardening@vger.kernel.org --- include/linux/randomize_kstack.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)